The usual method for the manufacture of thin film PV panels uses laser beams to scribe grooves through thin films deposited on large flat substrates. A PV panel consists of at least 3 thin film layers; a lower electrode layer, an active layer where light generates electricity and an upper electrode layer. At least one of the electrode layers is transparent so that light can reach the active layer. To increase the output voltage of the panel it is necessary to divide it into many separate cells which are electrically joined in series. The usual way to form and interconnect cells in thin film solar panels involves sequential layer coating and laser scribing processes. To complete the structure three separate coating processes and three separate laser processes are usually required. It is usual to perform these processes in a six step sequence consisting of a laser scribing step following each coating step. At each laser scribe step the requirement is to remove a single layer. The laser beams used for the 3 separate scribe steps can impinge on the substrate from either the coated side or if the substrate is transparent from the uncoated side.
In some cases this multi-step process is simplified by combining some of the separate layer coating steps. For example the lower electrode layer and the active layer (or layers) may be deposited sequentially and then both layers are scribed to form a groove through both layers. This is usually filled with an insulating material following which the interconnection procedure continues with a laser scribe through the active layer, deposition of the top electrode layer and a final scribe of the top electrode layer to isolate the cells. Thus there is a requirement in this case to scribe through 2 of the layers. The laser beam can impinge on the layers on the substrate from either the coated side of the substrate or if the substrate is transparent from the uncoated side.
WO2011/048352 describes a “one step interconnection” process in which all three layers are deposited before any laser scribing occurs. A first laser beam scribes through all three layers to form a groove which is filled with an insulating material. A second laser beam scribes through the top two layers leaving the lower electrode layer intact and conducting ink is applied to bridge across the insulator to connect the top electrode layer on one cell with the lower electrode layer on the adjacent cell. A third laser beam is used to scribe the top electrode layer to isolate the cells. Thus, in this case there is a requirement to make laser scribes through multiple layers to form the cell interconnection. WO2011/048352 also describes a “single combined process” in which all the cutting steps and ink jet processes are carried out in a single pass of the process head across the substrate. And as described in co-pending application GB (number not yet available), the laser beams used can impinge on the layers on the substrate from either the coated side of the substrate or, if the substrate is transparent, from the uncoated side.
The present invention seeks to provide a further improvement of these processes and of the apparatus used for carrying out the processes.